Currently the debugger implementation has three ways to restart a debug session:

• EH debugging: new rawDS is created and old rawDS is abandoned; DebugSession stays the same,
• restart without DAP restartRequest: DebugSession (and its rawDS) is terminated and new DebugSession (with new ID) is created with the heavy "startDebugging" API.
• restart with DAP restartRequest: DebugSession and rawDS is kept but if the preLaunchTask fails, and user requests to debug anyway a new DebugSession will be created on top of the still existing old DebugSession. This asks for trouble...

We need to fix this by following these principles and suggestions:

• the DebugSession and its ID must survive the restart. To achieve this we should use the EH Debugging as a model: DebugService.attachExtensionHost shows what needs to be done to reuse the DebugSession. Basically it just replaces the rawDebugSession by a new one.
• Ideally DebugService.restartSession should become similar to DebugService.attachExtensionHost because they do the same thing (and serve the same UI button).
• DebugService.runTask is used both for the postTask and the preLaunchTask but its implementation still assumes here and here that it is only meant for the preLaunchTask. runTask should better return a enum value to let its caller know what to do instead of doing it itself.